Abstract:Seriola has three species that are highly similar morphologically and are difficult to distinguish. Therefore, it is necessary to distinguish them by molecular biology methods. In this study, we explored the applicability of cytochrome oxidase subunit I (CO I), cytochrome oxidase subunit II (CO II), and 16S rRNA in identification and evolutionary analysis of the three species of Seriola, namely, S. lalandi (Chinese, Australian and Japanese populations), S. dumerili, and S. quinqueradiata. Three pairs of primers were designed for PCR amplification and sequencing of CO I, CO II, and 16S rRNA sequences of the three Seriola species. Dnasp5.10 and Mega7.0 software were used for DNA sequencing, genetic difference analysis, and phylogenetic tree analysis. The results showed that the CO I, CO II, and 16S rRNA sequences had a significant A+T bias. The mitochondrial 16S rRNA sequence was the most conservative, with a variation rate of 5.06%. The average number of nucleotide differences (k) and nucleotide diversity (Pi) according to the CO I sequence were higher than those of CO II and 16S rRNA. CO II had the highest haplotype diversity index among the three genes, indicating its high genetic diversity. The CO I sequence had higher differentiation and more abundant genetic resources than the 16S rRNA and CO II sequences. Thus, CO I and CO II sequences could be used to identify the three Seriola species in China and effectively identify the populations of S. lalandi from the three different waters (Northeast, Northwest and South Pacific waters). In the Seriola species, the interspecific genetic distances of CO I and CO II were more than 10 times the intraspecific genetic distances. The phylogenetic tree analysis showed that each species had independent branches. S. lalandi and S. quinqueradiata had a closer relationship than the others in the tree. The phylogenetic tree constructed using the three gene sequences could reflect the evolutionary relationship among the species. These results indicated that CO I and CO II gene sequences could be used as effective DNA barcodes for species identification and population division of Seriola species and provide efficient molecular tools for classification identification, resource screening, and diversity protection.

Abstract:To uncover the adaptative mechanism of the alkaline Amur ide (Leuciscus waleckii) population in Lake Dali Nor, Inner Mongolia, China, five samples of two populations, including one alkali form from Lake Dali Nor (DL), and one freshwater form from the Songhua River (SH), Heilongjiang, China, i.e., its historical origin, were analyzed using whole-genome resequencing technology. A total of 983528 nonredundant short insertions and deletions (InDels, 1–29 base pairs) were obtained. Among them, 8176 InDels that were polymorphic between the DL and SH populations were identified. Then, using integrated analysis of the known strong positive selection signal regions between the DL and SH populations, we identified a total of 176 potential candidate genes potentially affecting alkali-saline adaptation. Enrichment analysis showed that the genes were enriched mainly in inflammatory immune responses, ion transport, and osmotic regulation. Furthermore, the candidate genes abcc1, atp2b1, slc4a4, slc7a2, and aqp4 for key regulatory processes of alkali-saline adaptation, such as osmotic regulation and acid-base balance, were identified via selective pressure analysis using EasyCodeML, MEME, and FEL. Analysis showed that purifying selection played a dominative role for all of these genes, but a few amino sites could be identified to be under positive selection in the selection model. Prediction of three-dimensional structure revealed that some sites of the two proteins SLC4A4 and SLC7A2 coincided or were very close to the ligand-binding sites, indicating that the positive selection pressure mediated by the alkali-saline stress may contribute to the development of rapidly adaptive evolution in Amur ide. Our findings provide a basis for further study and reveal key genes for alkali-saline adaptation in Amur ide.

Abstract:In order to explore the role of stearoyl-CoA desaturase-1 (scd1) in the response of black porgy (Acanthopagrus schlegelii) to low temperature, the full-length cDNAs of scd1a and scd1b genes in the liver of black porgy were analyzed, and their expression in different tissues under acute low temperature stress was quantified. A temperature of 19.8 ℃ was used for the control group and 6 ℃ was used for the stress low temperature groups (cooling, at a rate of 1 ℃/h, to 6 ℃, which was maintained for 24 h). In the stress group, the individuals that could swim normally comprised the tolerant group and the ones in an unbalanced state comprised the sensitive group. The results showed that the full length of scd1a cDNA was 3281 bp (GenBank: No. MZ004439), including a 111-bp long 5′ non-coding region, 2162-bp long 3′ non-coding region, and 1008-bp long complete open reading frame, which encodes a total of 335 amino acids; the full length of scd1b gene cDNA was 1560 bp (GenBank: No. MZ004440), including a 1008-bp long complete open reading frame, encoding a total of 335 amino acids, and a 152-bp long 5′UTR and 400-bp long 3'UTR. The multiple sequence alignment results showed that the SCD amino acid sequences of black porgy and other bony fishes have a high degree of similarity (70%–98%), and both contain 3 highly conserved histidine elements. Phylogenetic tree analysis showed that the black porgy scd1a and scd1b genes were clustered with the A. latus scd and scd b genes, respectively, and there was a close evolutionary relationship between the two species. Using real-time quantitative polymerase chain reaction, it was found that at a water temperature of 19.8 ℃, Asscd1a and Asscd1b were mainly expressed in the liver, weakly expressed in the brain, and not expressed in the gills. The expression of scd1a in the liver was inhibited in the early stage and significantly up-regulated in the later stages (P＜0.05); scd1b expression showed a continuous up-regulation trend in the liver, while being up-regulated to higher levels than scd1a. This suggests that the regulation of expression of black porgy scd1a and scd1b genes is coordinated and plays a vital role in the acute low temperature response mechanism through different regulatory methods. The expression of Asscd1a and Asscd1b in the brain was inhibited, and in the gills, their expression was significantly up-regulated (P＜0.05). The two sub-types of scd1 in the tolerance group showed more rapid changes in the three tissues compared to the sensitive group. The dramatic changes in the expression of Asscd1a and Asscd1b indicate that they play an important role in the low temperature response of black porgy. The findings of the current study provide reference and supportive data for understanding the low temperature response mechanism and the breeding of cold-tolerant black porgy strains.

Abstract:To enhance our understanding of the mating process of the Chinese mitten crab, Eriocheir sinensis, the morphological functions of the copulatory system were observed and studied using flash-frozen samples, scanning electron microscopy, and histology. The copulatory system had the typical characteristics of Brachyura and belonged to the G1 long type. The male G1 was generally thick and smooth, in the form of a triangular column, with a suture groove formed by the overlap of the lateral margins of the endopodite, which contained a seminal canal and ran through the two ends. The base had one relatively large opening oriented towards the inner side of the dorsal surface, and the outer side was covered with a meat-like valve with feathery setae. During mating, the penis can extend into the outer part of the opening (or through a valve), and the inner part is inserted by G2. The distal end contained the other seminal opening, similar to a volcano mouth with bristle-like setae all around. G2 was small and sail-like, with the tip invaginated and four long transparent setae attached. The walls of both G1/G2 endopodites were different in thickness, and the seminal lumen of G1 corresponding to the G2 insertion part was thin. Therefore, the wall had a certain swelling capacity, and the lumen could be completely closed with the G1/G2 interaction during mating. Most of the G1 endopodite was hollow, and there were loose connective tissues with droplets above the insertable part of G2; correspondingly, many passages connected the lumen on the inner side of the tube wall. It could be inferred that there could be some form of communication between semen and G1 itself. Muscle tissue appeared in the latter half. The vulva was covered with a smooth and thick operculum, and the joint between the operculum and the thoracic segment of the mature individual could be easily shifted left and right to control the opening and closing of the vulva. The vagina was crescent-shaped in cross-section. One side of the chitinous wall was invaginated into the other, and thick muscles were attached to the invaginated wall. Finally, it can be concluded that G1 does not directly insert into the female reproductive tract but directly matches with the operculum and the surrounding thoracic segment. Through the co-evolution of G1 and G2, a “docking” mating system has developed to ensure that the sperm and other male materials are successfully transported into the spermathecae through the vagina for storage. This study described the potential internal cooperation mechanism of the copulatory system of E. sinensis, enriching the biological knowledge regarding crab insemination and providing theoretical and technical support for its genetic breeding and artificial insemination in the future.

Abstract:Hypoxia is a common stress phenomenon in aquaculture. Hypoxia tolerance of fish is an important indicator of fish resistance. To study the hypoxia tolerance of juveniles of tiger groupers (Epinephelus fuscoguttatus) and the hybrids, named jinhu groupers (E. fuscoguttatus♀×E. tukula♂), a closed breathing chamber was used to measure the oxygen consumption rate and suffocation point. In addition, the gradual hypoxia method was used to measure indicators of antioxidant enzyme activity and energy utilization in the liver by sampling the liver tissues of the individuals after 1 h at various dissolved oxygen levels [normal (5.71±0.31) mg/L, 4 mg/L, 3 mg/L, 2 mg/L, 1 mg/L, and 0.4 mg/L] and after 3 h at a normoxic level. The experimental results showed that when the water temperature was at (31.18±0.38) ℃, the oxygen consumption rate of jinhu grouper juveniles was 0.16 mg/(g·h), which was significantly higher than that of the female tiger grouper juveniles (P＜0.05). The suffocation points of tiger grouper and jinhu grouper juveniles were 0.22 mg/L and 0.24 mg/L, respectively, and the difference between the two species was not significant. During the process of decreasing dissolved oxygen concentration and returning to normal dissolved oxygen, there was a significant difference (P＜0.05) between superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and lactate dehydrogenase (LDH) enzyme activities and lactic acid (LD) content in the liver of tiger grouper juveniles, as well as SOD, catalase (CAT), GSH-Px, total antioxidant capacity (T-AOC), LDH enzyme activities in the liver of jinhu grouper juveniles. However, the activity change of T-AOC and CAT in the liver of tiger grouper juveniles and the content of LD in the liver of jinhu grouper juveniles were not significant. After 3 h of reoxygenation, the activity of SOD in the liver of tiger groupers increased by 16.7% and that of GSH-Px increased by 42.5%, while the content of LD increased by 2.8%. There were significant differences in these indicators between the reoxygnation group and the normoxic group (P＜0.05). However, there were no significant differences in the indicators of jinhu grouper juveniles compared with the normoxic group, except for the activity of GSH-Px (P＜0.05). During the change in dissolved oxygen level, the activation levels of SOD, GSH-Px, CAT, and T-AOC in the liver of jinhu groupers reached 29.1%, 17.9%, 42.4%, and 76.0%, respectively, which were higher than the maximum activation levels of corresponding antioxidant enzymes in tiger grouper livers. The experimental results showed that jinhu groupers had a slightly higher oxygen consumption rate than tiger groupers and that their hypoxia tolerance was higher. Thus, jinhu groupers can be cultured on a large scale and in high density. After being subjected to hypoxia stress, compared with tiger groupers, jinhu groupers could efficiently activate the antioxidant defense system to protect the body from oxidative damage and had a faster recovery ability after hypoxia.

Abstract:This study aimed to further understanding Coilia nasus germplasm resources, regarding aspects of cellular inheritance and biochemical inheritance, chromosome number, and karyotype structure of C. nasus, and to lay a theoretical foundation for screening the biochemical genetic markers of C. nasus germplasm. Short-term in vitro culture of gill filament cells was used to prepare chromosome specimens. Polyacrylamide gel electrophoresis was used to detect the expression of lactate dehydrogenase (LDH) in the heart, liver, kidney, eye, muscle, gill of C. nasus. The results showed that there was no difference in the number of chromosomes between males and females. The number of chromosomes was 2n=48, all of which belonged to terminal centromeric chromosomes (t), and the karyotype was 2n=48t. The number of arms (NF) was 48, and the sex chromosome type was ZW/ZZ. Unlike previous studies in which the karyotypes of C. nasus and C. brachygnathus were ZO/ZZ type, we found a “point” in the metaphase mitotic phase of the female chromosomes of C. nasus. Using mode analysis, we found that the probability of distribution of this “point” was more than 90.8% (120 metaphase mitotic phases), which was confirmed to be the female heteromorphic sex chromosome of Coilia species. A total of six LDH isoenzyme bands were detected in six tissues of C. nasus (heart, liver; kidney; eye, muscle; gill.), among which six bands were found in the liver tissue, with the lowest activity, and five bands were found in other tissues, with different activities. The expression of the LDH isoenzyme of C. nasus was tissue-specific. There were differences in LDH activity of C. nasus among different populations, in addition to individual differences. LDH is widely distributed in C. nasus and has obvious tissue specificity. The LDH enzyme band corresponding to expression in the eyes was highly expressed and presented stable activity, owing to which it can be used as a biochemical genetic marker for the identification of germplasm characteristics of C. nasus.

Abstract:In genome-wide association analysis of discontinuous traits, when complex population stratification exists in genomic data, the generalized linear model needs to consider hundreds of covariables at the same time, which slows the calculation speed and presents abnormal solutions. This study aimed to transform the effect value and heritability scale of significant loci in simple linear regression results into interpretable generalized linear regression results. First, the eigenvectors solved by spectral decomposition of the kinship matrix were considered as the principal components (PCs) to correct the population stratification in the discontinuous traits dataset. Then, a new covariate was formed through the sum of the multiplications of each covariate, and its regression coefficient of the principal component was computed using a linear regression model. The new covariate was used as the covariable of simple regression to carry out correlation tests for markers one by one. Finally, the generalized linear model was used for regression analysis of candidate quantitative trait nucleotides (QTNs), and the effects and variance were transformed into the generalized linear regression model scale. The genome-wide association analysis of sex reversal traits in half-smooth tongue sole (Cynoglossus semilaevis) was conducted using the new method and the generalized linear regression model with direct consideration of principal components: The results show that the QTN detection efficiency of this method is higher, a total of 6 QTNs were detected, including 5 QTNs on Z chromosome and 1 QTN on W chromosome. In addition, in terms of genome control, the genome control value of the method in this study is the same as that of the generalized linear regression model which directly considers PC, which is at an optimal level of 1.01. Therefore, the simple regression scaling transformation method based on principal component analysis improved the detection power for QTN detection, while retaining the accuracy of results, with fast and robust genome-wide association analysis of discontinuous traits. In addition, the QTNs detected by the new method proposed in this study can provide theoretical guidance for the study of sex reversal traits in half-smooth tongue soles.

Abstract:The yellowtail kingfish (Seriola lalandi) is a globally distributed marine economic fish. The consumer demand for this fish is growing because of its delicious taste and high nutritional value. With increasing catch numbers, its natural resources are gradually declining. Many countries, including China, have begun to artificially culture this species. We found that the development of the juvenile yellowtail kingfish gastrointestinal tract (stomach, pyloric caecum, and gut) was evident and strong, with a fast growth rate. Evaluating the characteristics of microbiota structure may contribute to analyzing the effect of the microbiota, introduced by feed, on the change rule of gastrointestinal tract microbiota during nutrient metabolism. In this study, 16S rDNA high-throughput sequencing was used to assess the characteristics of gastrointestinal tract microbiota structure of yellowtail kingfish juveniles during the whole feeding cycle and analyze the correlation with the microbiota in feed. Results showed that Lactobacillus, Pseudomonas, Acinetobacter, Sphingomonas, Bacteroides, Aeromonas, Vibrio, and Faecalibacterium were the shared and dominant genera colonizing the stomach, pyloric caecum, and gut. In combination with the changes in dominant genera during nutrient metabolism, Lactobacillus, Enterovibrio, Bifidobacterium, Pseudomonas, Acinetobacter, Bacillus, Escherichia-Shigella, Paenibacillus, Sphingomonas, Bacteroides, Methylomonas, Streptomyces, Aeromonas, Vibrio and Faecalibacterium were selected as the core microbiota in the gastrointestinal tract of yellowtail kingfish juveniles. These core microbiota contained both potential probiotics and pathogens; the relationship between the potential probiotics and pathogens in the gastrointestinal tract was maintained in a dynamic balance during nutrient metabolism of the host, which will protect the health of the host from a microecological perspective. Through analysis of the evolution trend of dominant microbiota structure, it was found that the microbiota introduced by feed had a great influence on the relative abundances of gastrointestinal tract microbiota during nutrient metabolism, which revealed the importance of the safety of the microbiota in feed. Our findings provide theoretical support for the screening of local probiotics of yellowtail kingfish juveniles and a reference for healthy culture management of the species.

Abstract:Stock enhancement is an effective method to achieve high production of the sea urchin Strongylocentrotus intermedius. This process is affected by various internal and external factors, among which temperature plays an important role. Temperature significantly affects the feeding and metabolism of S. intermedius, thereby regulating survival and growth. Temperature change, as an important stress factor, affects the behaviors of S. intermedius. These behaviors can effectively protect S. intermedius from the effects of environmental factors. The righting response, frequency of Aristotle’s lantern reflex, foraging behavior, positive phototaxis behavior, and negative phototaxis behavior reflect the behavioral functions of S. intermedius for foraging and self-protection against predators. Additionally, they are the most important adaptation-related characteristics for increasing the population size of S. intermedius. Therefore, it is essential to determine the optimal temperature range for stock enhancement of S. intermedius. In this study, S. intermedius were placed in temperature-controlled tanks. Stones were collected locally and placed in the tanks to simulate the benthic environment of S. intermedius. We placed large [(23.29±0.27) mm] and small [(18.78±0.19) mm] S. intermedius in three temperature environments (10 ℃, 15 ℃, and 20 ℃) for 6 weeks to observe the changes in their survival, growth and behaviors, to reveal the effects of different temperatures on S. intermedius. Growth referred to the change in body traits (test diameter, test weight, test height, crushing force of test, test thickness, body weight, lantern length, and lantern weight) and tissue weight (gonad weight and gut weight) of S. intermedius after 6 weeks. Behaviors included righting response, frequency of Aristotle’s lantern reflex, foraging behavior, positive phototaxis, and negative phototaxis. There was no mortality during the experiment. This indicates that 10–20 ℃ is an acceptable temperature range for the survival of S. intermedius. The food consumption of sea urchins in the 20 ℃ group was significantly higher than that in the other two temperature groups for both body sizes (P＜0.001). Test diameter, test weight, test height, crushing force of test, body weight, lantern length, lantern weight, gonad weight, and gut weight of different sizes were significantly lower in sea urchins exposed to 20 ℃ than to 10 ℃ and 15 ℃ Therefore, 10 ℃ and 15 ℃ were within the most suitable temperature range for optimal growth and development of sea urchins. Moreover, the frequency of Aristotle’s lantern reflex, phototaxis, negative phototaxis, and foraging behaviors of S. intermedius exposed to 15 ℃ was significantly greater than that at 20 ℃. This suggests that S. intermedius exhibits better behavior in this environment. In summary, the present study investigated the changes in survival, growth, and behaviors of S. intermedius at different water temperatures and found that 10–15 ℃ is appropriate for behavior and growth of S. intermedius. Releasing juvenile S. intermedius at 10–15 ℃ will maximize the benefit of stock enhancement. The present study provides valuable information for stock enhancement and resource management of S. intermedius.

Abstract:An 8-week experiment was conducted to evaluate the effect of fermented brewer’s yeast (Saccharomyces cerevisiae) supplementation on growth, feed utilization, and water quality in largemouth bass (Micropterus salmoides) farming. A diet containing 40% fish meal served as the reference (RF). In three other diets, 60% of the fish meal in the RF diet was replaced with cottonseed protein concentrate and supplemented with 0% (CH0), 1% (CH1), and 2% (CH2) fermented brewer’s yeast. The experiment was conducted in outdoor tanks, each containing 4000 L of aerated tap water. The initial body weight of the fish was (21.7±0.2) g (mean±SD, n=12), and stocking density was 30 fish per tank. During the experiment, water temperature was (22.5±5.2) ℃, dissolved oxygen was always more than 6.0 mg/L, and pH was (6.8±0.1). The fermented brewer’s yeast supplementation did not significantly affect the survival, weight gain, feed intake, feed conversion ratio, retention efficiencies of carbon and nitrogen, condition factor, hepatosomatic index, and body composition (moisture, crude protein, crude lipid, ash, carbon, and phosphorus content) of the fish as well as the levels of carbon, nitrogen, and phosphorus wastes; concentration of ammonia and total phosphorus; and chemical oxygen demand in the tanks (P＞0.05). Phosphorus retention efficiency declined with increasing fermented brewer’s yeast supplementation (P＜0.05). No significant differences were found in weight gain; feed intake; feed conversion ratio; retention efficiencies of carbon and nitrogen; contents of moisture, crude protein, and crude lipid in the whole body of the fish (P＞0.05). Moreover, carbon waste levels between fish fed the RF diet and those fed the CH0, CH1, and CH2 diets were not significantly different (P＞0.05). However, the ratio of fish meal consumption to fish production, hepatosomatic index, and body ash content in fish fed the RF diet was higher than that in fish fed the CH0, CH1, and CH2 diets (P＜0.05). Phosphorus retention efficiency was higher (P＜0.05), while the levels of carbon and nitrogen wastes were lower (P＜0.05) in fish fed the RF diet than in those fed the CH1 and CH2 diets (P＜0.05). Nutritional nitrogen accumulation was lower (P＜0.05), while phosphorus accumulation was higher (P＜0.01) than those calculated using the limnological method. This study reveals that dietary fish meal for largemouth bass can be reduced to 16% using cottonseed protein concentrate as a substitute. Adding 1% and 2% fermented brewer’s yeast to the diet did not significantly improve growth and feed utilization efficiency or reduce waste outputs in largemouth bass farming.

Abstract:In the present study, to isolate and screen a probiotic that degrades nitrite stably and efficiently, we carried out experiments on enrichment, isolation, culture, and identification of a suitable strain. Then, biological characteristics of the identified strain were determined through optimization of fermentation medium, analysis of nitrite degrading effect, and gene cloning of nitrite reductase. The strain was isolated and screened from five mixed water bodies, including aquaculture projects and wastewater treatment plants, and named JY-1. Additionally, the strain JY-1 was identified using 16S rDNA gene sequence analysis and physiological and biochemical characteristics. The results revealed strain JY-1 to be Bacillus gaemokensis. Optimization of fermentation conditions for sporulation of JY-1 strain indicated that the best carbon source for JY-1 was glucose and the best nitrogen source was tryptone. Analysis of the nitrite-degrading effect of JY-1 showed that JY-1 could degrade 0.6 mg/L nitrite in aquaculture water to 0.0 mg/L in 3 h. Moreover, the safety evaluation test suggested that no hemolysis was found, and the high concentration of JY-1 (109 CFU/mL) had no significant effect on the survival of Nile tilapia. Based on the results of experiments of gene cloning of nitrite reductase and the effect of JY-1 on ammonia, nitrite, and total nitrogen in water bodies, it is preliminarily speculated that enzymatic degradation, operated by JY-1, was the pathway through which nitrite was degraded and removed from water. In summary, this study provides an important basis for the preparation of microecological preparations with high efficiency in degrading nitrite.

Abstract:In order to investigate the contribution of basic food sources to Lateolabrax maculatus in three sub habitats of Jiuduansha salt marsh wetland in the Shanghai and to determine the stable isotope characteristics of carbon (δ¹³C) and nitrogen (δ¹⁵N) and the variation characteristics of basic food sources of this species, a survey was conducted in the mudflat, Scirpus mariqueter vegetation area and tidal creek from May to October in 2019. The results of one-way analysis of variance showed that there were no significant difference in δ13C among the three sub habitats. There were significant differences in δ15N between vegetation area and mudflat sub habitats, and there were significant differences in δ15N between vegetation area and the tidal creek sub habitat (P＜0.05). Increasing with body length δ¹³C and δ¹⁵N value showed an increasing trend, and δ13C value of L. maculatus in Jiuduansha salt marsh gradually increased each month, while δ15N value decreased sharply in July. The cluster analysis of monthly average δ¹³C and δ15N showed that July had little similarity with the other months (May, June, August, September, and October). The results showed that the composition and contribution rate of basic food sources in the three sub habitats are similar, and suspended particulate organic matter (POM) and Spartina alterniflora were the main carbon sources, followed by microalgae, Scirpus mariqueter and Phragmites australis contributed the least to the carbon source of maculatus. The contribution rate of POM decreased, while that of S. alterniflora increased with the increase in body length. With the growth of L. maculatus, the main food source for it changed from POM (＞70%) to POM (50%–66%) and S. alterniflora (32%–47%). The results showed that the feeding habits of L. maculatus changed in the juvenile stage. The contribution rates of carbon sources to L. maculatus in July were different from those in other months. The change was mainly caused by the sudden increase in the POM contribution rate and the decrease in the algae contribution rate. The internal reason may be affected by the Yangtze River runoff. Conclusion: there were no significant differences in the composition and contribution rate of basic food sources of L. maculatus among the three sub habitats, but there may be differences in the feeding in different sub habitats; During the growth process, the basic food source of of L. maculatus in the three sub habitats changed from POM to POM and S. alterniflora, which may be due to the change of feeding habits of L. maculatus during the growth process.

Abstract:Since decades, there have been no reports on the fish resource of the Tibet reach of the Lancang River, China. To gain a contemporary understanding of the corresponding fish communities, field surveys on fish resources were conducted in the main stream and major tributaries of the Tibet reach of the Lancang River in April and September 2017, April, July, and October 2018, and April and September 2019. Fish samples were caught using drifting gillnets (mesh size: 2.5 cm and 7.0 cm). A total of 13 fish species from 2 orders and 5 families (subfamilies) were collected with 9 indigenous fish species and 4 exotic fish species. Omnivorous and carnivorous fishes accounted for 92.3% and 7.7% of total fish, respectively. Benthic and slow-flowing fishes accounted for 61.5% of the fish species. Schizothorax lissolabiatus, S. lantsangensis, Ptychobarbus kaznakovi, and Schizopygopsis anteroventris were the dominant species. The Shannon-Wiener index, Pielou evenness index, and Margalef richness index of the fish community were 0.570–1.249, 0.585–0.901, and 0.504–1.423, respectively. In general, the fish community structure of the Tibet reach of the Lancang River was simple and stable. All historically recorded indigenous fishes were sampled, while all exotic fishes were recorded for the first time. To protect the indigenous fish resources in the Tibet reach of the Lancang River, it is suggested to strengthen the habitat protection, artificial domestication, and breeding of indigenous fishes, as well as to focus on the control of exotic fish populations and prevent invasion.

Abstract:To explore the relationship between the temporal and spatial characteristics of larval Ctenopharyngodon idellus and hydrological factors in the Anqing section of the lower Yangtze River, the larval C. idellus were systematically monitored from April 2018 to August 2020. A total of 272 larval C. idellus were identified using morphological and molecular biological methods, of which the three-year catch accounted for 12.30%, 34.52%, and 4.37% of the four major fish catches in China in 2018, 2019, and 2020, respectively. According to the estimation of larval fish resources, their runoffs were 3.95×108 , 5.79×108 , and 3.29×108 , for 2018, 2019, and 2020, respectively. The results of spatial and temporal characteristics analysis showed that the larvae and juveniles of C. idellus were present mainly from May to July, with peaks in May and the early part of mid-July. In 2020, the abundance of larvae and juveniles of C. idellus was the lowest because the flood was not suitable for breeding and because the main flood season was delayed. Kruskal-Wallis test showed that the abundance of larval C. idellus on the left and right banks was significantly higher than that in the middle of the river (P＜0.05, n=70). From 2018 to 2020, the spatial distribution of the overall average abundance was distributed as follows: left bank (8.99 ind/1000 m3)＞right bank (5.34 ind/1000 m3)＞middle of the river (3.53 ind/1000 m3). Pearson correlation analysis showed that the abundance of larval C. idellus was significantly positively correlated with water temperature, the daily rising rate of water level, and runoff and negatively correlated with transparency. GAM model analysis showed that the relative importance of hydrological factors was as follows: water temperature＞transparency＞daily rising rate of water level＞daily rising rate of runoff. In this study, the total deviation interpretation rate of the GAM model reached 90.8%, which accurately revealed the response relationship between the abundance of larval C. idellus and hydrological factors. This study accumulated basic data for understanding the occurrence mechanism of early C. idellus resources in the Yangtze River.

Abstract:To study the immune efficacy of inactivated vaccine of heterologous Streptococcus agalactiae extracellular product in tilapia (Oreochromis niloticus), two strains of S. agalactiae (HN0901 and GX1101) were cultured, and highly efficacious vaccines were developed using extracellular products and formalin-killed whole cells of HN0901 and GX1101. The vaccine was administered by intraperitoneal (i.p.) injection in a volume of 0.2 mL, and sham-vaccinated (control) fish were i.p. injected with the same volume of sterile BHI. At 28 d post-vaccination (DPV), the fish were challenged, i.p. injection, with approximately 1.0×108 CFU of homologous or heterologous S. agalactiae to determine the efficacy of protective immunity. The immune response and serum antibody titer of the immunized and post-injected tilapia were measured, and the relative immune protection rate and cross-immune protection rate were compared. The results showed that the alanine aminotransferase and aspartate aminotransferase levels of immunized fish were significantly higher than those of control fish at 28 DPV but significantly lower than those of control fish post injection. Compared with the control fish, the levels of superoxide dismutase and catalase in immunized fish increased in varying degrees after immunization and challenge, while malondialdehyde levels decreased significantly (P＜0.05). The results of real-time quantitative polymerase chain reaction also indicated that TNF-α, IL-1β, TGF-β, HSP 70, MHC , Ⅱ and IgM expression levels showed different degrees of significant increase and were higher than those in the control group after immunization and challenge (P＜0.05). Serum antibody titer reached 1 : 6400 at 28 DPV, which was significantly higher than that of the control group (P＜0.05). The relative percentage of survival ranged from 31.6% to 47.4% after the homologous or heterologous S. agalactiae challenge. Furthermore, the developed inactivated vaccines significantly induced an immune response in tilapia and produced moderate vaccine efficacy. Administration of the single isolate HN0901 or GX1101 vaccine via i.p. injection was marginally protective in preventing streptococcal disease caused by homologous or heterologous isolates of S. agalactiae. Our findings laid a foundation for further studies on immune prevention technology against streptococcosis in tilapia and the development of bivalent vaccines.